Catalytic cracking and refining of hydrocarbon oils



Feb@ 24, 1948. C, W, TYSQN CATALYTIC CRACKING AND REFNING OF IIYDROCARBON OILS Filed Aug. 14, 1942 Patented Feb. 24, ,1948

CATALYTIC CRACKING AND REFINING F HYDROCARBON OILS Charles W. Tyson, Summit, N. J., assignor to StandardOil Development Company, a corporation of Delaware Application August 14, 1942, Serial No. 454,753 y "z claims. (ci. 19e- 49) This invention relates to the catalytic conversion of hydrocarbon oils and is directed more particularly to a continuous process for cracking oils in which the cracking is carried out in the presence of a finely divided powdered catalyst.

While the invention in some of its broader aspects has a more general application, it is particularly adapted to a two-stage cracking process wherein the petroleum oil is first cracked to form a naphtha fraction, and the naphtha fraction or a selective cut therefrom is then' subjected to treating to improve the quality thereof.

It has been proposed heretofore to crack higher boiling hydrocarbons in the presence of finely divided catalyst to form lower boiling hydrocarbons in the motor fuel boiling range. According to the general procedure followed, when employing this general type of process, the oil to be cracked is first passed through a cracking zone containing the nely divided cracking catalyst at a controlled velocity to maintain a dense turbulent mass of catalytic material within the cracking zone. Following the cracking treatment, the cracked products are separated from the nely divided catalytic material and thereafter fractionated to condense the insufficiently cracked constituents therefrom, The initial condensate formed during the latter fractionation contains the entrained catalytic material present in the cracked vapors so that the resulting distillate product resulting from the fractionation is virtually free of entrained solids and no additional purification treatment is necessary to remove solids therefrom.

More recently it has been discovered that the quality of the gasoline, and particularly the aviation fraction, may be materially improved with respect to its acid heat, lead response and other quire further separation to remove the entrained catalytic material.

One of the primary objects of the present invention is to provide a method of removing entrained finely divided catalytic material from vapors resulting from the treating or reforming of low-boiling distillates, such as naphtha, which 2 contain little if any constituents boiling above the end point of the final product.

It has also been proposed heretofore, when cracking in the presence of finely divided catalysts, to supply a large proportion of the heat required for the process by circulating the catalytic material through a regenerating zone in which the catalyticlmaterial is heated t0 a temperature susbtantially above the desired cracking temperature and then transferring the hot, regenerated catalyst back to the cracking zone. During the regeneration treatment, the catalyst is heated by burning carbonaceous deposits formed on the catalytic material during the cracking operation. This method of operating materially reduces the capital investment for a cracking unit of given capacity by eliminating the furnaces for preheating the oil and also by eliminating the cooling tubes which might otherwise be necessary for removing heat liberated during regeneration. The process also reduces the operating costs by utilizing a low-grade fuel formed during the cracking process to supply the heat required for the operation.

However, when operating in this manner, it is usually necessary to limit the temperature to which the catalyst is heated during regeneration in order to avoid permanently impairing the activity of the catalytic material. In many cases,

the maximum permissible temperature to which4 the catalytic material may be heated without impairing its activity is not greatly in excess of the temperature desired for carrying out the cracking process. For example, in most of the active catalysts employed at the present time it is desirable to maintain the regeneration temperature below the maximum of 1150 F. or 1200 F., whereas in many cases it is desirable to carry Vout the cracking process at temperatures of the order of from 900 F. to 1050J F. Since the temperature to which the catalyst may be heated during regeneration is not greatly in excess of that required for the cracking process, it is necessary to circulate large quantities of catalytic material continuously through the cracking and regeneration zones in order to supply the heat required for the cracking operation. For this reason it is important to provide some means of preheating the oil to the maximum permissible temperature without requiring the use of external heating coils or other extraneous devices which would further increase the cost of the cracking equipment.

Another important object of the present invention is to provide an improved method wherein V ed catalytic material.

A further object of the invention is to provide a method of preheating the fresh oil from the process and at the same time remove entrained catalytic material from the cracked gasoline vapors.

Other more detailed objects and advantages 1o of the invention will be apparent from the detailed description hereinafter in which reference will be made to the accomparwing drawing which is a diagrammatic illustration of an apparatus forming a part of the present invention and capable of carrying out the process forming another part thereof.

In accordance with the broader phases of the present invention, the oil to be cracked is first passed in direct contact with hot cracked products resulting from the cracking or reforming of low-boiling gasoline or naphtha fractions which contain little if any constituents within the boiling range of the oil to be cracked. The fresh charging oil passing in countercurrent contact with the hot cracked vapors cools the cracked vapors, removes entrained catalytic material contained therein, and at the same time preheats the oil for the cracking process.

Referring particularly to the drawing, the reference character III designates a chargeline through which the oil to be cracked is introduced into the system. This oil may be a clean condensate stock, such as a gas oil, or it may be a residual oil, such as a topped or reduced crude. In some cases it may be a total crude which contains little if any gasoline constituents.

The oil introduced through line I0 is passed into the top of a combined scrubbing and, cooling tower II through which cracked vapors resulting from the cracking of low-boiling hydrocarbon distillates, such as naphtha, are passed as hereinafter described. The scrubbing and cooling tower I I may be provided with suitable baiiles for eiecting more intimate contact between the cracked vapors and the fresh charging oil or it may be a conventional bubble tower capable of eiiicient fractionation. The fresh charging oil passing in countercurrent contact with the cracked vapors is preheated by the direct contact therewith. The tower II may contain a body of fresh oil through which the vaporous products pass before being 'removed therefrom. The temperature of the oil in the base of the tower may be regulated by pumping a portion of the oil collected in the base of the tower through line I2' to cooler l2" and returning it to the top of the tower. For example, the cracked vapors introduced into the scrubbing tower may be at a temperature of the order of from '700 F. to l000 F. 60 and the fresh oil introduced therein may be preheated to a temperature of from 400 F. to 700 F.

To avoid intermixing of the fresh feed with the cracked vapors, the vapors should boil sub-- stantially outside the boiling range of the feed 55 and the mixing temperature should be substantially above the dew point of the vapors. Under such conditions, the fresh feed after contacting with the cracked vapors will be substantially free of cracked products and the cracked products will be substantially free of feed constituents.

The fresh charging oil after passing through the combined scrubbing and cooling tower II is removed from the bottom thereof through line I2 and continues through line Il into which is 75 the amount of catalytic material so introduced.

The catalytic material introduced into the oil,v

stream passing through line Il may be any suit# able cracking catalyst, such as naturally active or activated clays and synthetic gels comprising silica-alumina, siiica-magnesia, silica-zirconia,

and boric oxide alumina. This catalytic matea rial may consist solely of active catalytic components, or the catalytic components may be diluted with relatively inert material, such as sand, diatomaceous earth, clays, or the like, which have little if any catalytic activity but which may serve as a heat carrier for transferring heat from the regeneration' zone into the cracking zone, as later described. This catalytic material preferably has a particle size ranging, for example, between 0.1 and microns. The temperature of the catalytic material introduced into the oil stream passing through line I4 should be substantially above the temperature desired forthe cracking operation and the amount of catalytic material introduced should be sufficient to heat the oil from the initial preheat temperature before described to the final desired cracking temperature and to supply the necessary heat for the cracking reaction. The temperature ofthe catalytic material introduced into the oil stream is substantially the temperature maintained during regeneration of the catalytic material which,

in turn, may be of thevorder of from 1000" F. to 1200I7 F., and preferably about 1150 F.

The cracking process may be carried out at a temperature ranging from '250 F. to 1000 F. The amount of catalytic material necessary to heat the oil from its initial preheating temperature to the desired reaction temperature may be of the order of from 5 to 40 parts of catalytic material per part of oil by weight.

In many cases this relatively large amount of catalytic material necessary to supply the necessary heat may result in undesirable side or chain reactions. For this reason, it may be of advantage in many cases to dilute the catalytic material with relatively inert material, as previously described.

The oil upon contact with the hot regenerated catalytic material is vaporized and heated to the desired reaction temperature. The resulting mixture of catalytic material and oil vapors then continues through line I4 to a catalytic converter II. This mixture preferably discharges into the converter I1 through a centrally located discharge nozzle I8 positioned in the bottom section of the reactor. The nozzle I8 is also preferably spaced from the outer wall of the reaction chamber and is provided with a. perforated grid plate I9 for distributing the mixture of oil vapors and catalytic material over substantially the full cross-sectional area of the converter. The space between the outer wall and the nozzle i8 forms an annular passage through which catalytic material to be regenerated may pass into a stripping or settling section 2l positioned below the inlet nozzle I8.

The Velocity of the oil vapors passing upwardly through the converter I1 after issuing from the nozzle I8 is preferably controlled so as to permit the finely divided catalytic material to settle into a relatively dense mass which is maintained in a turbulent condition similar to a boiling liquid by the upward passage of the oil vapors through the mass. The velocity of the oil vapors passing upwardly through the converter II may; for exam- Y ple, be oi' the order of from0.2 to 5.0 feet per second.

Spent catalytic material after being retained within the converter ll for the desired length of time is withdrawn therefrom through an outlet conduit 22 positioned at the bottom of the converter. The rate of withdrawal oi' the catalytic material from the converter is preferably controlled to maintain the relatively dense mass of catalytic material at a level substantially below the top of the converter, such as from to 15 feet or more. By permitting a relatively iree space above the dense mass of catalytic material, the amount of entrained powderpassing overhead with the cracked products issuing from the top of the reactor may be materially reduced.

The height of the dense mass of catalytic material maintained within the converter il is regulated to obtain the desired contact time between the cracked vapors and catalytic material within the converter. This contact time may be oi the order of from 5 to 50 seconds, depending upon the nature of the catalyst, the temperature, the characteristics of the oil treated, degree of conversion desired, and other factors..

The cracked vapors containing a small amount l of entrained catalytic material are removed from the top of the converter il through line 23. The amount of entrained powder contained in the cracked vapors will dependupon the size and density of the catalyst particles, the velocityl of the oil vapors passing through the catalyst mass within the converter, the amount oi' free vspace provided above the level of the dense catalytic mass within the converter, and other factors. However, under properly controlled conditions, the amount of such entrained material may be reduced to such a point that it can be readily removed from the bottom section of the fractionating tower. However, if desired, additional separating equipment, such as cyclones, may be located in the top section of the catalytic converter or in the transfer line 2t.

The cracked vapors removed trom the converter il through line 2t pass into the bottom section of -a product fractionator 2d in which the cracked products are fractionated to condense insumciently cracked constituents as reflux condensate. The initial condensate formed in the fractionating tower 2d will contain the entrained catalytic material carried overhead from the converter through line 23. This initial condensate may be removed from the bottom of the fractionating 'tower through line 25 and may be passed through line 26 and pump 2l and combined with fresh feed passing through lines i2 and it.

The cracked vapors passing into the fractionating tower 2d are normally at a temperature substantially above the dew point. As a result, it is necessary to provide means for cooling the cracked vapors to below its dew point in order to condense .the insuiciently cracked constituents. To accomplish this cooling, a portion ofthe initial condensate removed from the bottom of the tower 2t through line 25 may be passed through line 2d and pump 29 to a cooling coil t! and thereafter returned to the fractionating tower through line 32 at a point above the point of entry of the cracked vapors. 'This recycling and cooling of the initial condensatev from the bottom of the fractionating tower may serve as a scrubbing medium for removing entrained solids from the cracked vapors and also for cooling the cracked vapors to the dew point.

The fractionating tower 2l may be provided with one or more trap-out trays 33 for segregating the cycle oil into various fractions, such as heating oil, kerosene, or the like. This cycle oil may be withdrawn from the vtrap-out tray through line 34 and may be subjected to recracking or may be withdrawn from the system as a nal product of the process. .v

The -top temperature oi.' the fractionating tower 24 may be controlled to take overhead the total gasoline and lighter constituents, or it may be maintained at a lower temperature to condense a heavy naphtha fraction. In the latter case, the naphtha fraction may be collected in separate trap-out tray 35 which may be withdrawn therefrom through line 38. A

Vapors remaining uncondensed after passage through the fractionating tower 2t and which may comprise the total gasoline constituents boiling below 400 F. or a selective lower boiling fraction just mentioned are removed overhead from the fractionating .tower 2d through line 31 and passed to a condenser t8 wherein they are cooled l to a-temperature sumcient to condense the normally liquid constituents contained in the vapors. Products from .the condenser 3d may then pass to a low-pressure product receiver 39 in which the liquid condensed in the condenser 38 is segregated from the uncondensed gases and vapors.

The'cracking Yprocess is preferably carried out at a relatively low pressure, such as from substantially atmospheric to 3 or 4 atmospheres. Under such conditions, the receiver 39 will also be under a pressure below the cracking pressure. As a result, the bulk of the butane-butene constituents will remain in vapor form after passage through condenser 38, and substantial amounts of pentane-pentene constituents may also be in vapor form. f

Vapors and gases separated from liquid distillate in receiver 39 areA Withdrawn overhead .through line All. The liquid distillate separated from the gases from receiver 39 is removed therefrom through line t2. 'Ihe liquid distillate withdrawn from receiver t9 through line d may be directly subjected to further treatment to reduce the amount of olens contained therein. To this end, the liquid distillate `from line di may continue through line t3, pump ed into line l5 into which finely divided catalytic material discharges through conduit es having a feed valve fit.

As illustrated, the catalytic material discharging from conduit t6 into line d5, carrying the liquid distillate from receiver 39 isof the same composition a-s that employed in the initial catalytic cracking process and is obtained from the same regenerator later to be described. The amount of hot regenerated catalytic material introduced into the distillate stream in line it should be suclent to heat the distillate to the desired retreating or reforming temperature, which may be of the order of from 500 F. to 1000 F.

The purpose of the second treatment as just mentioned is to reduce the acid heat of the product by increasing the amount of saturated constituents contained therein. This results in a substantial improvement in the lead response and reduces the amount of lead required for a nal product of given octane. For example, an aviation fuel of octanewith the addition of l cc. of tetraethyl lead per gallon may be obtained by the retreating of this distillate under the conditions above mentioned. This improvement in acid heat and lead response is obtained by reasses duction in the olefin content of the distillate fraction. The exact reason for the reduction in the amount of oleflns by retreating of the distillate formed in the initial cracking operation is not fully understood but may be attributed to the polymerization of the oleilnlconstituents or to the transfer of hydrogen iroml` the more saturated constituents or alkylation of the oleilns. The cleans contained in the distillate receiver d2 are largely concentrated in the lower molecular weight hydrocarbons, such as in the butanobullene, pentane-pentene, and hexane-hexene components. In view oi this, the ltop temperature of the fractionating tower 2s may be con-:- trailed as previously described to condense all of the constituents boiling above hexane-hexene, or the liquid distillate in the tower 38 may be subjected to further fractionation.l to segregate a light naphtha fraction consisting largely of constituents below hexane-hexene and this latter fraction may be subjected to treatment rather than the total naphtha fraction. Furthermore, in some cases it may be desirable to include in the fraction which is subjected to further treatment some higher boiling hydrocarbons. For example, the fraction passing through line d5 may be a fraction having an end point above 400 F. To thisl end, the top temperature of the fractionating tower 24 may be controlled to take overhead not only the 400 F. end point constituents but also constituents boiling, for example, up to 500 F. Furthermore, it may be desirable in some cases to segregate a light naphtha such as a fraction containing principally hexanehexene constituents and lower boiling hydrocarbons and also a fraction having constituents boiling between 300 F. and 400 F.; in other words. a fraction in which a. center cut boiling between 170 F. and 300 F. has been removed. It has been further found, for instance, that the frac tion of the cracked distillate resulting from the catalytic cracking treatment previously described having a boiling range between 200 F. and 300 F. consists principally of aromatic constituents which are not improved by subsequent catalytic treatment. Consequently, it may be of advantage to remove this fraction from the distillate prior to subjecting it to the second catalytic treatment.

The hot regenerated catalytic material discharging from conduit 4d into the distillate stream through line 45 vaporizes and heats the distillate to the desired reaction temperature. The resulting mixture continues through line 45 into a second catalytic converter 41 through an inlet Ynozzle 48. The second catalytic converter may be of the same general construction as that previously described with reference to the cracking converter i1 so that no further detailed description is necessary. This converter may be materially smaller than the cracking` converter l1 since the distillate charged into the converter comprises only a fraction of the total feed charged into the cracking converter I1. The oil vapors passing through the second converter 41 are likewise preferably controlled to maintain a dense catalytic mass therein which is kept in a violently agitated state by the upward passage of the vapors therethrough. The catalytic material after being retained within the second converter 41 for the desired period is withdrawn from the bottom thereof through conduit 49. The catalytic material is removed from the converter 41 at a rate such as to maintain the level of the dense mass within the converter 41 at a substantial distance below the vapor outlet communicating with the top of the converter. as previously described in connection with converter l1. so as to reduce the amount of powdered material en trained in the vapors removed from the converter. II'he oil vapors are retained in the second converter #il for a period sufficient to obtain the desired improvement in the quality of the product. The contact time of the oil vapors with the catalyst in the converter el may, for example, range between 2 and 50 seconds. lThe treated vapors after. passing through the second converter i1 are removed therefrom through line 5i and are passed into the cooling and scrubbing tower li previously described through which they pass upwardly in countercurrent contact with the fresh charging oil. This direct contact between the fresh charging oil and the cracked vapors from the converter #l1 serves to cool the cracked vapors and preheat the oil. ln addition, the fresh heavier charging oil serves to remove any entrained powdered catalyst contained in the cracked vapors removed from the converter d1. If desired, cyclones or other suitable separators may be provided either in line 5i or in the top section of the converter #i1 for further removal of entrained powder from the cracked vapors prior to introduction into the scrubbing tower il. However, under properly controlled conditions the amount of entrainment carried overhead through line 5i from the converter d1 will be sufciently small so as to permit complete removal therefrom by the scrubbing oil introduced into scrubbing tower ll through lille i0.

Since the treated vapors passing into the scrub- .bing tower il are vapors resulting from the cracking of the low boiling constituents having a. boiling range below the boiling range of the fresh feed passing to the cracking operation, the oli vapors removed from the scrubbing tower H will be substantially free of fresh oil constituents and the fresh oil constituents removed from the scrubbing tower il will be substantially free of cracked products. To this end, it is important, however, that the charge passing into the scrubblng tower il be substantially free of virgin gasoline or constituents boiling within the boiling range of the feed passing to the converter 61'.

The cracked vapors after passing upwardly through the chamber li in contact with the fresh oil are removed from the scrubbing tower through line 52 and may pass directly to a condenser 53 in which the vapors are condensed to liquefy normally liquid constituents of the cracked vapors. 'I'he products from the condenser -53 may be then passed through line 56 to a product receiver 55 in which the liquid distillate formed in the condenser 53 separates from uncondensed gases and vapors.

The retreatment carried out in the converter 41 is also preferably under relatively low pressure such as from substantially atmospheric to from 3 to 4 atmospheres and the receiver 55 is also preferably at a pressure somewhat lower than that maintained in the converter 41. As a result of the relatively low pressure maintained in the receiver 55, the bulk of the butane-butene, and even substantial amounts of pentane-pentene constituents, will remain uncondensed after passage through the condense;` 53 unless subnormal temperature is maintained therein. As a. result. the vapors liberated from the liquid distillate in receiver 55 will contain the bulk of the butanebutene constituents and substantial amounts of the pentane-pentene constituents. The vapors and gases separated in the receiver 55 are re- `moved therefrom through line 56 and the liquid distillate is removed therefrom through line 51.

This latter product may be withdrawn throughline 58 as` a final product of the process or it may be remixed with compressed vapors from the receiver 55 through line 56, as later described.

Returning to the catalytic cracking converter I1, the catalytic material after being retained in the main body of the reactor I1 for the desired period discharges through the annular space between the inlet nozzle I8 and the outer wall of the reactor into the bottom section 2 I' into which may be discharged an inert stripping gas through line 6I. This stripping gas may serve to remove any volatile hydrocarbons contained in the catalytic material which'is to be Withdrawn from the converter I1 through conduit 22. The spent catalytic material containing carbonaceous deposits resulting from the cracking treatment discharges from the bottom section 2I of the converter I1 into the conduit 22 as previously described and is fed through a control valve 62 into a stream of air passing through line 63 which serves as a carrier for transporting the catalyst through line 64 into the regenerator 6-5. The regenerator 65 may be provided with -an inverted cone-shaped bottom having a grid 68 positioned above the cone. The mixture of air and catalyst to be regenerated may be introduced in the bottom section 61 of the regenerator 65 below the perforated grid 66 so that the grid serves to distribute the mixture of regenerating air and catalytic material throughout the full cross-sectional area of the regenerator 65. The catalytic material and air pass upwardly through the grid line 66 into the body of the regenerator 65.

The velocity of the regenerating air passing upwardly through the regenerator 65 is preferably controlled so that the catalytic material tends to settle into a relatively dense mass which is maintained in a state of continuous agitation by the upward passage of the regenerating gas therethrough. The density of this lmass maintained in the regenerator and also that maintained in the catalytic converters in practical operations may be between and 30 pounds per cubic foot, depending upon the type of catalyst, size of the particles, and other factors.

The air upon contacting with the spent catalytic material, which is at substantially the temperature of the cracking treatment, serves to burn oi the carbonaceous material contained on the catalyst. This burning treatment results in heating the catalytic material during the regeneration as previously described. However, it is necessary to avoid heating the catalytic material in the regenerating zone to such a tem- .perature which would impair the activity thereoi.

The amount of fuel, in the form of carbonaceous deposits, contained on the catalyst may in many cases be more or less than that required for carrying out the cracking operation. Where the amount of carbonaceous deposits formed during the cracking operation is insufficient to supply the required heat for the cracking and recracking operations, additional heat may be provided by further heating the catalytic material prior to returning it to the cracking zone. This may be accomplished by adding extraneous fuel to the regenerator or by further heating of the catalytic material passing to or from the regenerator.

Where the amount of fuel, in the form of carbonaceous deposits formed during the cracking operation as previously described, is greater than that required for carrying out the cracking process, some additional means may be necessary for removing the excess heat liberated during the regeneration treatment. However, a considerable flexibility in the amount of heat required to be carried into the oil stream by the hot regenerated catalyst may be obtained by regulating the preheating temperature of the oil prior to mixing with the catalytic material. For example, in cases where the operation results in the formation of excessive quantities of carbonaceous deposits, a portion or all of the fresh charge may be by-passed around the scrubbing tower II in which the charge is normally preheated by cracked vapors from the converter 41. The pump back circuit previously described consisting of line I2' and exchanger I 2, may be used in this case to remove the excess heat from the tower. By regulating the preheating temperature of the fresh feed mixing with the cracking catalyst, it is possible in practical operations, in most cases at least, to supply the bulk of the heat required for the process by burning of the carbonaceous deposits from the catalytic material during the regeneration treatment.

The catalytic material after being heated to the desired degree within' the regeneration chamber 65 may be withdrawn therefrom through a `conduit 68 positioned in the bottom of the regenerator 65 and having a vertical extension 69 projecting upwardly through the grid plate 66 into the main body of the regenerator 65. The catalytic material from the regenerator 65 continuously ows downwardly through the extension 69 into' the conduit 68 from which it may be passed into the vertical conduits I5 and 46 for return to the catalytic converters I1 and d1. respectively. The catalytic material is preferably withdrawn from the regenerator which will maintain the level of the dense catalytic mass within the regenerator materially below the top of the regenerator so as to maintain a relatively free space thereabove. The regenerating gas after passing through the main body of the finely divided catalytic material in the regenerator may be passed into a suitable separator such as a cyclone separator 10 located in the top of the regenerator for further separation of entrained powder therefrom. The regenerating gas after passing through the cyclone separator 10 may then continue through outlet line 1I to a cooler 1E in which the regenerating gas may be cooled from the regeneration temperature to a temperature of the order of from 300 F. to 600 F. Products from the cooler 12 may be then passed through line 13 into a suitable separator such as a Cottrell 1d for further separation of the entrained powder therefrom. The catalytic powder separated in the Cottrell 1d may discharge through line 15 into an air streampassing through line 16 and may be returned through line 11 to the regenerator 65. Regenerating gas after passing through the Cottrell 1t may be vented to the atmosphere through stack 16 or it may be scrubbed with a cooling liquid such as oil or water for further purication before being vented to the atmosphere.

Returning again to'the low-pressure receiver 39 receiving the products overhead from the fractionator 24, as previously mentioned, this receiver operates at relatively low pressure so that the overhead gases removed from the receiver contain a considerable amount of low-molecular weight, normally liquid constituents, such as butane-butene, propane-propone, and pentanepenf Y square inch vand thereafter mixed with the raw l tene constituents. .To V-recover these valuable constituents from the gases, the gaseous products from the receiver 39 may be compressed in a compressor 80 to a pressure of from-100 to 300 pounds per square inch and afterwards mixed with a portion or all of the liquid distillate from the receiver 39. To this end, liquid distillate from the receiver 39 may be passed through lines 42 and 8| and pump 82 and then admixed with the compressed gases in line 831. The mixture from line 83 may be passed into a cooling coil 84 while under a pressure of from 100 to 300 pounds, as previously described. Under these higher pressure conditions, the low-molecular weight, normally liquid components from the initial gases withdrawn from the receiver 39 may be combined with the liquid distillate. Products from the condenser 84 may lre then passed to a highipressure receiver 85 in which the liouid separates from the gaseous constituents. The distillate collected in receiver 85 under such conditions will contain the bulk of the lower molecular weight, normally liquid products previously mentioned, and the gaseous products separated in the high-pressure receiver 85 vill contain a materially lower concentration of the lower molecular weight, normally liquid hydrocarbons. The gases separated from the distillate in the highpressure receiver 85 may be removed through line 86 and passed to a suitable fractionating and absorption equipment for separation of this gas into the desired components. such as propanepropene, ethane-ethene, andthe like.

The liquid distillate separated in the highpressure receiver 85 may be passed through line 81 to a debutanizing tower 88 in which the distillate may be subjected to pressure distillation to vaporize the butane-butene constituents and lower boiling hydrocarbons. The vapors formed inthe debutanizing tower 88 and remaining uncondensed therein may be' removed overhead through line 89. Liquid remaining unvaporized in the debutanizing tower 88 may be removed therefrom through line 9|. This debutanized product may then be passed through line 92 to line 45 and pump 44 to the second-stage catalytic converter 41. Under such conditions, the feed to the converter 41 may comprise a mixture of the raw distillate from the low-pressure receiver 39 and the debutanized distillate from the debutanizing tower 88, or all of the raw distillate from receiver 39 may be rst debutanized before being subjected to further catalytic treatment. In order to supply the required heat for distilling the lower boiling hydrocarbons from the distillate in debutanizing tower 88, a portion of the distillate removed from the bottom thereof may be passed through line 93, pump 84 and reboiler 95 wherein it is heated to a temperature suiicient to supply the requiredV heat for the distilling treatment. The 'heated distillate after passing through the reboiler 95 may be then returned to the debutanizing tower 88 through line 9S at a point above the discharge of the distillate discharging through line 81.

Returning again to the low-pressure receiver 55 which collects the liquid distillate from the second-stage catalytic treatment', the products from this receiver may be treated as previously described to segregate the lower boiling constituents. For example, the overhead gases and vapors from the receiver 55 containing substantial amounts of the lower molecular weight liquid hydrocarbons may be compressed in compressor 91 to a pressure of from 100 to 300 pounds per liquid distillate from the bottom of receiver 55. This distillate may, for example, pass through line 98 and pump 90 andrthereafter combined with the compressed vapors in line |0|. The resulting mixture may then be cooled in condenser |02 and thereafter passed to the high-pressure receiver |03. The gaseous products consisting principally of hydrogen and low-molecular weight hydrocarbons, such as propane-propene, and lower boiling hydrocarbons may be removed from the high-pressure receiver |83 through line |04 and passed to suitable fractionation and absorption equipment forl separation of the desired com.. ponents therefrom. The liquid distillate in receiver |03 which contains the major portion of the butane-butene and higher boiling constituents is removed from the high-pressure receiver .trap-out tray |08 for segregating an aviation gasoline distillate from the higher boiling constituents. The higher boiling fraction is removed from the bottom of the stabilizing tower |05 through line |01. This product may comprise a motor fuel fraction of the desired boiling range and volatility or it may comprise a heavy naphtha fraction boiling above the end point of aviation motor fuel. The heat required for the stabilizing treatment may be provided by passing a portion of the liquid distillate withdrawn through line |01 through line |88, pump |09 into a reboiler l I8 in which the oil is heated toA the required temperature. The distillate after passing-through the reboiler ||0 may then return to the stabilizing tower |05 through line III at a point above the discharge of the unstabilized distillate discharging through line |84'. The vapors liberated in the stabilizing tower |85 and consisting principally of the butane-butene fraction and lower boiling constituents are removed from the top of the stabilizer |05 through line I2. This product may be combined with the overhead product from the debutanizing tower 88 and the combined mixture subjected to further fractionation and absorption treatment for separation of desirable components therefrom. Under present conditions, the butane-butene fraction formed in the process forms a valuable product for the production of alkylate for aviation gasoline, as a source material for the production of synthetic rubber, and for other types of chemical products.

' While I have shown for illustrative purposes the use of the same type of catalytic material rial for,.promoting other types of hydrocarbon reactions, such as hydrogenation, polymerization, isomerization, and alkylation. catalytic material employed for these operations are generally known and need not be referred to here in detail. It is preferred, however, to employ the same type of catalyst for carrying out The types of -.will be intermixed with the fresh charging oil passing to the cracking operation. Consequently,

in continuous operations the catalyst from the retreating reactor will tend to become intermixed with the catalyst from the cracking reactor.

In operations of the character above described wherein the iinely divided catalytic material is circulated continuously through the system, it is necessary to provide means for restoring pressure on the catalyst during circulation. For example, in such a circulating system, there is inherently a certain drop in pressure due to the ilow of the material through the equipment. This pressure must be restored in order to return the catalytic material and maintain the desired circulation. As illustrated, this pressure is restored by passing the catalytic material through suitable standpipes of a height which will develop a hydrostatic pressure suflicient to restore the pressure on the catalytic material being circulated.

For example, the conduits i5 and d6 employed ior returning the hot regenerated catalytic ma.- terial from the regenerator to the converters I1 and lll, respectively, may be utilized as a standpipe for developing .the necessary pressure to overcome the pressure diiierence between the regenerator and the cracking zones and also to provide a substantial pressure drop across the feed valves i6 and d6 located in the conduits i5 and t6.

In order that the conduits I5 and d6 may serve as a standpipe for developing hydrostatic pressure, it is important to maintain the catalytic material flowing therethrough in a iluidized, freely flowing state so that the pressure may be transmitted throughout the full length of the conduits. The finely divided powdered catalytic material may be maintained in a freely flowing fluidized state necessary for developing hydrof` static pressure by keeping a small amount of an aerating or iiuidizing gas in intimate mixture with the catalytic material passing through the conduits. To this end, it may be necessary to introduce a small amount of aerating or iiuidizing gas at one or more points along the conduits l5 and 56 to maintain it in fluidized condition. This aerating gas may, for example, be introduced along the conduit i5 through lines H5, i IB and ill. Likewise, a fluldizing gas may be introduced into column t6 through lines lit, il@ and i20. In some cases, where the circulation of the catalytic material is relatively rapid the amount of gas occluded in the catalytic material being withdrawn from the reactor and regenerator may be sumcient to maintain the material in a highly fluid, mobile condition Without the necessity of adding an additional fluidizing gas.

The pressure necessary for passing the catalytic material from the converters il and tl into the air stream passing through line 6d may also be obtained by hydrostatic pressure developed on the catalyst during its passage through the conduits 22 and 39, respectively. A fiuidizlng gas may also be introduced into these conduits at spaced points lto maintain the catalytic material in fluidized state during its passage therethrough.

Referring to the second catalytic converter 1, the catalytic material after being retained therein for the desired time, which may be of the order of from 15 seconds to 10 minutes or more, is passed continuously through the annular space formed between the inlet nozzle 48 and the outer wall of the converter l1 into the bottom section of the converter. This bottom section forms a stripping zone into which a stripping gas, such as carbon dioxide, steam or other inert gas, maybe introduced through line i22. The spent catalytic material then discharges from the bottom section oi the converter 41 through line 49 intothe air stream 64 which serves as a carrier for transferring it to the regenerating zone.

While a common regenerator has been shown for regenerating the catalytic material withdrawn from both the second converter tl and the initial )converter i1, it will be understood that, if desired, each converter may be provided with its own regenerator. This is, of course, necessary whenever the catalytic material in the converter 41 is of a different composition than the catalytic ma terial used in the converter I'i.

While a specific type of cracking equipment has been described in detail for carrying out the process, it will be understood that the invention in some of its'broader phases may be carried out in equipment materially diierent from that described. For example, some phases of the invention might be employed in operations in which -a fixed static bed of catalytic material is maintained in the individual reactors and the catalytic material subjected to alternate cracking and regenerating treatments. However, the invention in its narrower phases has particular application to operations in which the catalytic material is continuously passed through alternate cracking and regenerating zones.

Having described the preferred embodiment of the invention, it will be understood that it embraces such other variations and rnodilcations as come within the spirit and scope thereof.

What is desired to be protected by Letters Patent is:

1. A process for the conversion of hydrocarbon oils which comprises passing a relatively heavy oil boiling above the end point of naphtha through a cracking zone maintained at active cracking temperature above about 700 F., contacting said oil within said cracking zone with a finely divided catalytic material, keeping said oil in contact with said catalytic material for a period suflicient toobtain the desired cracking thereof,- thereafter separating the cracked products from the catalytic material, fractionating the cracked products to segregate a naphtha fraction therefrom, passing said naphtha fraction through a rening zone maintained at a temperature above about 500 F., contacting said naphtha fraction while in vapor form within said last-named refining zone with an active refining catalyst, keeping said naphtha vapors in contact with said refining catalyst for a period suiiicient to obtain the desired rei-ming treatment thereof, thereafter separating the bulk of said lnely divided refining catalyst from the reiirxed vapors. and thereafter passing the refined vapors containing entrained refining catalyst while at substantially said refining temperature in contact with fresh oil which is subjected to said first-named cracking treatment.

2. The invention defined by claim 1, wherein the catalytic material employed in said refining zone is of the same composition as that employed in the cracking zone.

3. A process for the conversion of hydrocarbon oils which comprises passing a relatively high boiling hydrocarbon oil boiling above the boiling range of naphtha upwardly through a cracking zone containing a body of iinely divided catalytic material, regulating the velocity of the oil vapors passing upwardly through said body of catalytic material to maintain a dense turbulent mass of catalytic material Within said cracking zone, keeping said cracking zone at a temperature above about 709 F.. maintaining said oil vapors in contact'with said nely divided catalytic material within said cracking zone for a period suicient to obtain the desired cracking thereof, thereafter removing cracked vapors from said cracking zone, fractionating the cracked products to segregate a naphtha fraction therefrom, passing said naphtha fraction upwardly through a refining zione containing a body of finely divided catalytic material, regulating the velocity of the vapors passing upwardly through said last-named rening zone to maintain a dense turbulent mass of finely divided catalytic material therein, keeping said reiining zone at a temperature above about 500 F., maintaining the naphtha vapors in contact with said catalytic material within said refining zone for a period suiilclent to obtain the desired refining thereof, thereafter removing the rened naphtha vapors containing entrained catalytic material from said refining zone, and passing said naphtha vapors removed from said refining zone upwardly through a body of said higher boiling oil to be subjected to said rstnamedv cracking treatment to thereby remove entrained catalytic material from said naphtha vapors and to preheat said higher boiling oil.

4. The process defined in claim 3, wherein the catalytic material employed in said refining zone is of substantially the same composition as that employed in said cracking zone.

5. A process for the conversion of hydrocarbon oils which comprises passing a relatively heavy oil boiling above the naphtha boiling range while in vapor form upwardly through a cracking zone containing a body of finely divided catalytic material, controlling the velocity oi the oil vapors passing upwardly through said body of catalytic material to maintain a relatively dense turbulent mass of catalytic material therein, keeping said cracking zone at active cracking temperature above about 700 F., continuously removing catalytic material from said cracking zone containing carbonaceous deposits resulting from said cracking treatment, passing the catalytic material so Withdrawn to a, regenerating zone, subjecting the finely divided catalytic material within said regenerating zone to oxidizing atmosphere to burn off carbonaceous deposits contained thereon and thereby heating said catalyst above the cracking temperature, returning the regenerated catalytic material while at substantially its regeneration temperature to the cracking zone, fractionating the cracked products to segregate a naphtha fraction therefrom, passing said naphtha fraction upwardly through a rening zone containing a mass of iinely divided catalytic material of the same composition'as that contained in said cracking zone, regulating the velocity of the naphtha vapors passing upwardly through said refining zone to maintain a dense turbulent mass of said catalytic material therein, keeping said refining zone at a temperature above about 500 F., maintaining said naphtha vapors in contact with said catalytic material for a period suiilcient to obtain the desired refining thereof, thereafter removing the treated vapors containing entrained finely divided catalytic material from said refining zone, passing said treated naphtha vapors through a body of said rst-named heavier oil to be subjected to said cracking treatment to thereby preheat said oil and remove entrained catalytic material from said naphtha vapors, and fractionating said naphtha vapors to segregate the desired distillate therefrom.

6. The process deilned in claim 5, wherein the catalytic material is continuously removed from said refining zone and passed to said regenerating zone for removal of carbonaceous deposits formed during the refining treatment and wherein a portion of the regenerated catalyst from said regeneration zone is returned to said rening zone.

7. The process dened by claim 5, wherein the catalytic material is circulated through said cracking zone by hydrostatic pressure.

QHARLES W. TYSON.

REFERENCES CITED The following references are of record in the nie of this patent:

UNITED STATES PATENTS 

